Before the cookieless future starts: how to use cookie syncing effectively in 2025?

The flight to a cookieless future is delayed—for now. Despite Google’s repeated announcements to deprecate them, both third-party cookies and cookie synching are still alive and kicking across Chrome. Their effectiveness, however, is declining by leaps and bounds. Can this be fixed? In a sense, yes. That's what we'll discuss in this guide. We’ll also unpack the benefits, expose the pitfalls, and explain some specific details you could miss. 

First thing first: What is cookie syncing?

Cookie syncing is a mechanism used in programmatic advertising to match user IDs between different platforms—like SSPs, DSPs, and data providers. Here's how it goes:

The SSP puts a cookie file in their browser. This file contains an unique user ID to identify the users in the future. The DSP and Ad Exchange (or DMP/DCP if they are involved in the network) use their own cookies to track users. In the end, a single user may have multiple IDs assigned to them by several platforms. When the bidding starts, the SSP/Ad Exchange and the DSP must ensure they are bidding for the same user and avoid duplicate bids. This is why cookie syncing exists. It helps to match IDs between SSPs/Ad Exchanges and DSPs to ensure they belong to the same user.

Inside the sync: How IDs actually get matched

The whole process may vary depending on the number of involved partners, strategy, and technical solutions they use, but in general, it includes these stages: 

1. A user visits a website. 

2. The publisher (SSP or ID provider) checks the user's ID and assigns it if the user doesn't have one. 

3. The SSP initiates cookie syncing with an ad exchange or DSP to match the user's ID with theirs. They do it by comparing IDs in their match table (a database where each partner stores its own set of user IDs). Since each partner typically maintains its own table, syncing ensures that IDs refer to the same user across different platforms. The matching process often involves pixel requests or redirects when multiple partners are involved.

4. After matching IDs and successfully identifying a user, the SSP sends a bid request to the Ad Exchange or DSP. The request contains matching IDs, so the Ad Exchange or DSP can reference it to retrieve additional user data.

What are the benefits?

DSPs can’t recognize users without checking their IDs. Cookie sync solves this issue and maintains the higher performance of programmatic auctions. There are, however, other advantages that benefit all parties involved, like:

For demand partners:

Increased targeting abilities and conversions. Cookie sync is the simplest way for advertisers to deliver personalized ads, thereby attracting more users. With it, they can target even specific audiences, such as, for example, females of a particular age from specific locations who prefer regular sports activities. Advertisers can also retarget users who have already purchased their products, either to exclude them from the bidding process or to offer them other products to encourage repeat purchases.

For supply partners:

Increased revenue and ROI. Helping the DSP to track users, the SSP improves the quality of the bidding process. This, in turn, enhances revenues as DSPs tend to bid higher for users they already know and thus have higher chances of getting a conversion.     

What are the challenges?

Using third-party cookies has its risks too, which also negatively impacts cookie sync performance. They include:

Privacy leaks 

Most users don’t like the idea of someone collecting their data, so more and more people prefer not to share information about their internet activity. Privacy regulations like GDPR, which require websites to share which data they collect and for what reason, only motivate users to reject cookies even more. As a result, websites gather less data now, and this impacts the cookie-syncing process. Matching IDs has become a significantly complicated task, resulting in more failures

Browsers’ restrictions

While Google is delaying its deprecation of third-party cookies, Safari and Firefox have already done it, limiting websites’ ability to collect them. This makes it challenging for advertisers to set up targeted advertising. Moreover, users now use multiple devices simultaneously. As a result, the same person may watch the same ads from a tablet and laptop, but track it rather hard if using only third-party cookies.

Security and performance issues

Third-party cookies are often placed on websites without obtaining the consent of their owners. This also may happen during synchronization operations, especially if many partners are involved. This poses several risks for such websites, including performance decrease (having too many cookies slows down web page loading) and security vulnerabilities, as unauthorized cookies may track sensitive users’ data.

How to minimize those risks?

The best recommendation here is to start to prepare for a cookieless future and, therefore, pay greater attention to first-party data and contextual targeting tools. On the other hand, third-party cookies continue to play a significant role in programmatic advertising, and many companies rely on them. So, to help them navigate through our not-ready-to-ditch-cookies world, here’s a short list of recommendations to improve your cookie-syncing experience: 

1. Monitor the cookie syncing operations. Ensure you and your partners are on the same page regarding cookie sync configuration and send each other the correct requests. Mistakes in the cookie sync requests are the most common reason for synchronization failures. 

2. Choose partners for cookie sync carefully. Focus on syncing with partners that provide the most valuable data and have a reliable reputation for avoiding the risk of unauthorized cookie installation. Also, ensure all your partners have match tables to keep users’ IDs and update them regularly. 

3. Control domains involved in the cookie sync process. Remove old, unneeded, or unknown domains to prevent domain spoofing and other fraud risks.

4. Explore Cookieless ID Alternatives. As third-party cookies decline, consider experimenting with emerging ID solutions like UID 2.0, RampID, or SharedID. These frameworks offer privacy-compliant ways to maintain user identity resolution without depending on traditional cookies -- making them more sustainable in the long run.

5. Use efficient and reliable programmatic technologies. The quality and performance of your cookie syncing operations depend on it. Moreover, cookie syncing setup can be tricky as it requires all partners to work as one and quickly fix issues from their end. That is why Teqblaze’s white-label SSP+ad exchange    platform provides full custom support whenever you need help. For example, there are cases when cookie syncing fails because one of the partners didn’t set it up or send HTTP requests that contain invalid parameters. Our custom support team helps to identify such issues and fix them. 

      

To sum up

Cookie syncing remains crucial to maintaining effective communication between SSPs/Ad Exchanges and DSPs and enhancing the bidding process. It also helps marketers target their ads to specific audiences without significant costs or efforts.

Having said that, privacy and security concerns surrounding third-party cookies keep making cookie synching less effective. And the future remains uncertain: cookies may not disappear tomorrow, but the downfall is inevitable. So, while trying to squeeze maximum value out of cookie sync, don’t delay your preparation for life without cookies—before it’s too late!